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Posted: May 17, 2010

Brightest X-ray machine in the world probes molecules

(Nanowerk News) The Stanford Linear Accelerator Center (SLAC), long the preserve of particle physics, is also a major laboratory for conducting experiments in fields like biology and medicine. The electron acceleration equipment has been adapted over the past few years to create something known as the Linac Coherent Light Source (LCLS), which produces short X-ray pulses millions of times brighter than those currently created by other instruments.

The LCLS is the brightest X-ray machine in the world for the energies at which it operates -- with photon energies in the "hard X-ray" region and very high beam intensities of 10^18 watts per square centimeter. At these energies, the LCLS machine can serve as an excellent microscope for viewing matter at the scale of atoms, and biologists, chemists, and physicists have been eager to do exactly that. It also acts like a knife since it can pare electrons away from the parent atoms and molecules, even those huddling very close to the nucleus.

Becoming operational last fall, the first experimental results from the LCLS are starting to appear at scientific meetings. In San Jose, Li Fang of Western Michigan University will report on how the powerful LCLS X-rays can be used to strip electrons away from a nitrogen molecule. He says that in the extreme case, nitrogen atoms were detected from which all of the electrons had been removed. This causes the molecule to quickly dissociate. The plucked electrons, which nearby detectors can spot and measure, allow researchers to calculate the binding energy within the original molecule. In future experiments, more and more such measurements will give experimenters a more accurate assessment of large molecules, especially bio-molecules.